Abstract
The most important advantage of multiuser detectors is that they can degrade multiple access interference and increase system performance efficiently. However, they also change mean and variance of each user’s decision statistic in the same time. In fact, decision statistics of system outputs are not longer time-invariant either. Therefore, the conventional single-user Viterbi decoder may be further improved.This paper will propose modified algorithms for the decoders used in conjunction with polynomial receiver and linear successive interference cancellation (LSIC) receiver for DS- CDMA systems with long spreading sequence. The modifications are based on explaining the detected signal as asymptotic Gaussian and calculating time-dependent mean and variance accurately by matrix algebra. In addition, an approach method of the mean and variance is also presented and put to use in the modified decoding algorithm. The performance gains of the modified Viterbi decoders will be shown in the paper.